1. Field of Invention
The present invention pertains to the field of information storage units. More particularly, this invention relates to an information storage unit using a layer adjacent the storage layer to affect data detection.
2. Background
Electronic devices, such as palm computers, digital cameras and cellular telephones, are becoming more compact and miniature, even as they incorporate more sophisticated data processing and storage circuitry. Moreover, types of digital communication other than text are becoming much more common, such as video, audio and graphics, requiring massive amounts of data to convey the complex information inherent therein. These developments have created an enormous demand for new storage technologies that are capable of handling more complex data at a lower cost and in a much more compact package.
One response to this demand has been the development of ultra-high density storage devices, such as the one described in U.S. Pat. No. 5,557,596 granted to Gibson et al. on Sep. 17, 1996. This system provides for a plurality of electron emitters generating beams of electrons to information storage media areas on a movable platform to store and retrieve information. A micro mover, based on micro electro mechanical systems (MEMS) technology moves the platform relative to the electron emitters to enable parallel communications with selected storage media areas on the platform. In the Gibson et al patent, an electron beam impacts storage media areas at different intensities, selectively altering some aspects of the storage material, such as changing the state of the storage material between amorphous and crystalline phases or between different crystalline phases that affect the response of the storage medium to a readback stimulus, such as the response of a diode storage medium to a readback electron beam.
There is a continued need for increased miniaturization and expanded ability to handle greater quantities of more complex data at a faster speed and in even more compact areas. The industry is moving towards the storage of data in the range of tens to hundreds of nanometers.
Several challenges arise in attempting to store data at this level. The processes of information storage and retrieval become increasingly difficult tasks, and writing and reading data with electron beams presents several limitations. It is possible to use low energy electrons in this technique to avoid problems with dielectric breakdown, field emission from undesirable locations, and the need for relatively large and expensive power supplies. However, data detection becomes difficult because low energy electrons have very short penetration depths, making this approach highly susceptible to the surface conditions of the medium. Moreover, only very thin layers may be present on the top of the storage media, making difficult the use of a protective layer or a conducting electrode on top of the storage layer. In addition, the stability and cyclability of a storage device using electron-readback may be limited by the mechanical and thermal properties of the free surface of the storage medium. Only very thin protective cladding layers can be used with a low-energy electron-beam addressing scheme, as thicker layers would prevent access by low energy electrons.
In some miniature storage devices, such as CD-RW and DVD-RW drives, data is written and/or detected using directed light beams, such as lasers, to reversibly change the optical reflectivity of a storage medium. As data storage densities and miniaturization increase, the diffraction-limited spot size of the lasers sets a lower bound to the size of bits to be written. However, this diffraction limit can be circumvented using near-field light sources that provide evanescent light emitted through a small aperture. In such systems, data may be detected by impacting the storage area with a photon beam and then detecting the flow of electrons, holes or photons (hereinafter called “carriers”) emitted from the data storage area. An example of using a directed light beam system for reading data in a high-density storage device by detecting carrier flow is shown in our co-pending patent application entitled “Data Storage Media Utilizing Directed Light Beam and Near-Field Optical Sources” (U.S. Ser. No. 09/865,940 filed on May 25, 2001).
The storage of data at substantially increased densities gives rise to problems in the task of reading the data. High-density storage devices make sensing data increasingly difficult because of interference from neighboring non-selected memory cells and because the flows of electrons, photons or holes generated from the sensing process are so small that detection becomes extremely difficult and errors in data detection increase.
Accordingly, to read miniature data cells in high-density memory storage, it is desirable to develop techniques capable of producing greater amounts of carrier flows and more effective methods of converting energy from light or electrons to detectible carriers. Memory structure and methods are needed to store and read high-density data so that detection of data is more readily obtained.